1. Field of the Invention
This invention relates to a cling wrap plastic film formed from polyethylene.
2. Description of the Prior Art
Household food wraps may be produced from various polymers including low density polyethylene. The desirable properties of film-type food wraps include the following:
(1) "Cling"--how well the film stays wrapped around food such as sandwiches and adheres to open containers for food such as glass bowls.
(2) High strength characteristics such as tensile strength, puncture resistance and Elmendorf tear.
(3) High stretch capability--how hard the film may be stretched and elongated without breakage.
(4) Good handleability--how well the film resists tangling during use.
(5) "Cutter bar tear"--how readily a length of the film may be withdrawn from a carton and severed by ripping or cutting on the carton's cutter bar.
The cling property is typically enhanced by the use of cling additive in the film. Also, the film-type food wraps are customarily produced in thin gauges such as 0.5 mil in thickness, for economy and to provide a limpness so that the film may conform to the various shapes of packaged or wrapped containers, bowls and foods. With such thin film, toughness becomes a problem and manufacturers of film-type food wraps are constantly seeking to improve this property.
Consumers are also interested in the ease of dispensing and tearing off a sheet of film as it is withdrawn from a container that the film is packaged in. For this purpose, containers such as cartons are ordinarily provided with sharp edges, usually, a saw-tooth edge, known as a "cutter bar". Manufacturers have attempted to comply with this consumer demand by supplying film that can be withdrawn from a container to a desired length and severed along the cutter bar with ease.
With the introduction of "linear" low density polyethylenes made by low pressure processes (hereinafter referred to as "LPLDPE"), attempts have been made to substitute this material for cling wrap film applications in place of conventional highly branched low density polyethylenes made by high pressure processes (hereinafter referred to as "HPLDPE"). The reason for these efforts is that LPLDPE is widely recognized as being tougher and stronger than HPLDPE (reference: "Process Engineering News", February 1980, pg. 33). However, it has been determined that LPLDPE does not provide one of the important properties required in cling wrap plastic films--ease in cutter bar tear off. Even at 0.5 mils thickness, LPLDPE film is very difficult and in some instances impossible to tear off in the transverse direction of the film on conventional cutter bar strips. The film tends to elongate, and considerable effort and energy are required to sever the film.
Accordingly, it is an object of this invention to provide a cling wrap polyethylene film which has high strength, high stretch capability and ease of cutter bar tear off.